Displacement measuring means



.fimg; mg WW E1. sPANGLER ET W fi DISPLACEMENT MEASURING MEANS DriginalFiled Nov, 25, 1962 "PGTEN 7' I O/M'E TIFF? MW *MCE'ELEWOMETTERFQEQUENCY United States Patent 3,266,302 DISPLACEMENT MEASURING MEANSElson B. Spangler, Bloomfield Hills, and William J. Kelly,

Clawson, Mich, assignors to General Motors Corporation, Detroit, Mich, acorporation of Delaware Continuation of application Ser. No. 23%,708,Nov. 23,

1962. This application June 9, 1965, Ser. No. 462,650 7 Claims. (Cl.73-4105) This application is a continuation of Serial No. 239,708, filedNovember 23, 1962, now abandoned.

This invention relates to means for measuring displacements and moreparticularly for measuring displacements of a body subjected to variablefrequency motion in a given direction.

Frequently, applications arise wherein it is desirable that means beprovided for accurately measuring displacements of a body which issubjected to variable frequency motion in a given direction. Forexample, when designing vehicle suspension systems, road simulators arefrequently used to simulate actual road conditions. Such a simulator maytake the form of an electromechanical device wherein input electricalsignals taken from a magnetic tape representative of a particular roadprofile are used to actuate mechanical means connected with a vehiclesuspension system in a manner to simulate actual road conditions. Insuch an application it is important that an accurate system be used formeasuring the road profile to be recorded on the magnetic tape. One formof the prior art for measuring road profile includes a vehicle adaptedto be towed by another vehicle over the surface of a road under study.An accelerometer is mounted on the towed vehicle responsive toacceleration thereof in a given direction and operative to develop anoutput signal variable in accordance therewith. Suitable computing meansare connected with the accelerometer for developing an output signalvariable in accordance with the extent of the displacements of the towedvehicle in the given direction. However, the device described does notaccurately measure displacements of the vehicle due to surfaceundulations or waves extending over a range from low frequency-longwaves to high frequencyshort Waves. This is true because anaccelerometer which is responsive to displacements of the vehicledue tohighfrequency short wave surface undulations must be capable ofmeasuring large acceleration forces. The use of such an. accelerometerresults in poor noise to signal ratio when used for measuringacceleration due to low frequencylong wave displacements of the vehicle.

In accordance with this invention, means are provided for accuratelymeasuring the profile of a surface with respect to an inertial referenceplane by the displacements of portions of a body which is passed overthe surface thereby to be subjected to variable frequency motion in agiven direction. This is accomplished by providing a frequency selectivecoupling between the surface to be measured and motion sensing means forpurposes of transmitting motion of low frequency to the motion sensingmeans and attenuating motion of higher frequency. The motion sensingmeans, which may take the form of an accelerometer with suitableintegrators, is operative to develop first output signals in accordancewith motion of the body with respect to the inertial reference plane at.the low frequency. Measuring means are also provided for developing asecond output signal variable in accordance with the extent of relativedisplacements between the portion of the body carrying the motionsensing means and the surface. Accordingly, the output signals developedby the motion sensing means and the measuring means may be summed withsuitable means to obtain an output signal variable in accordance withthe extent of displacements of the body throughout the frequency rangeof body motion.

A more complete understanding of this invention may be had from thedetailed description which follows taken with the accompanying drawingin which:

FIGURE 1 is a schematic representation of one embodiment of theinvention, and

FIGURE 2 is a graphical representation illustrating the total frequencyrange of operation.

Referring now to the drawing and more particularly to FIGURE 1, there isshown a towed vehicle 10 including a rotatable member in the form of awheel 12 rotatably mounted to a wheel support 14 and adapted to traversethe surface of a road 16. A vehicle platform .18 is provided havingmounted thereon on one side a cylindrical member 20 coaxially alignedwith a similar cylindrical member 22 mounted on the wheel support 14. Ahelically shaped coil spring 24 coaxially surrounds both members 20 and2-2 with one end mounted on the support member 14 and the other endmounting the platform 18. The spring 2 4 supports the weight of theplatform 18 and the plunger member 20' as Well as a mass 26 mounted onthe other side of the platform 18.

A tow rod 30 is provided having one end pivotally mounted to a supportmember 32 mounted on the rear of a towing vehicle 34 and having itsother end rigidly connected with the platform 18. Wheel holddown meansare provided for exerting a hold-down force on the wheel 12 and includea rigid member 36 securely fastened in centilever fashion to the rear ofthe towing vehicle 34 and a coil spring 38 interposed between the towrod 30 and the member 36. The spring 38 is preferably biased so that itprovide a force moment acting in a counterclockwise direction about thepivot support means 32, as depicted in FIGURE 1, to provide sufficienthold-down force on the vehicle 10 to maintain the periphery of the wheel12 in frictional contact with the surface of the road 16 as the wheeltraverses the road. In one embodiment of the invention, a wheelhold-down force approximately ten times the weight of the vehicle 10 wasfound to be sufficient to maintain the periphery of the wheel in contactwith the surface of the road.

In accordance with this invention, surface undulations of the road 16are measured by measuring displacements of the wheel 12 normally of andwith respect to a reference direction as the wheel traverses andmaintains contact with the road. The reference direction may take theform of a plane 40 parallel to the average slope of the road 16 over thedistance of road surface to be studied. Displacements of the wheel 12with respect to the plane 40 are designated as W, as indicated inFIGURE 1. Furthermore, in order to accurately measure the displacementsW throughout the frequency range of urface undulations of the road 16the spring 24 serves as frequency selective coupling means adapted totransmit acceleration of the wheel 12 to the mass 26 below apredetermined or break frequency and to attenuate acceleration above thepredetermined frequency. Acceleration of the wheel 12 of a frequency inexcess of the predetermined frequency will result in relativedisplacements between the wheel 12 and the platform 18 as the vehicleIt) traverses the road 16. Hence the surface undulations of the road 16may be represented by:

26 normally of and with respect to the plane 40 due to a displacement Wof the wheel 12 resulting in an acceleration below the break frequencyof the spring 24;

Y is the second order time derivative representing the acceleration ofthe mass 26 normally of the plane 40 due to a change of position Y ofthe mass 26; and

(W-Y) is the relative displacement between the mass 26 and the wheel 12due to a displacement W of the wheel 12 resulting in an accelerationexceeding the break frequency of the spring 24.

Equation 1 may be solved electrically with the following apparatus. Theacceleration Y of the mass 26 normally of the plane 40 is measured withan accelerometer 28 which is mounted on the mass 26 and has a volt-agesource 42 connected between ground and an input terminal 29 of theaccelerometer. The accelerometer 28 is responsive to acceleration of themass 26 normally of the plane 40 below the break frequency of the spring24 and is operative to develop an output signal voltage Y between groundand an output terminal 44 of the accelerometer which varies inaccordance with acceleration of the mass. Preferably, the accelerometer28 exhibits a low noise to signal ratio for low frequency-long waveacceleration below the break frequency of the spring 24. The outputsignal voltage Y of the accelerometer 28 is applied between ground andan input terminal 46 of computing means in the form of an integratingdevice 48. The integrating device 48 is responsive to the output signalvoltage Y and is operative to perform a double integration thereof anddevelop an output signal voltage Y between ground and an output terminal50 of the integrating device which varies in accordance with the extentof the change of position Y of the mass 26.

Displacement measuring means in the form of a potentiometer 52 isprovided between the wheel 12 and the accelerometer 28 for purposes ofdeveloping an output signal voltage (W-Y) which varies in accordancewith the extent of relative displacement (W-Y) between the mass 26 andthe wheel 12. The potentiometer 52 includes a resistance element 54having a voltage source 56 connected thereacross and a wiper arm 58. Theresistance element 54 and the. wiper arm 58 are mechanically mounted tothe wheel support 14 and the tow rod 30, respectively, in the manner asshown in FIGURE 1 so that the resistance element 54 is in slidableengagement with the wiper arm 58 in a plane approximately parallel tothe longitudinal axes of members 20 and 22. Since it is desirable thatthe output signal voltage (W-Y) be indicative of the relativedisplacement (W-Y) between the wheel 12 and the plat-form 18 due to adisplacement of the wheel normally of the plane 40', it is preferablethat the tow rod 30 be so positioned to maintain the longitudinal axesof members 20 and 22 approximately perpendicular to the plane 40. Theoutput signal voltage (WY) of the potentiometer 52 is obtained betweenground and the wiper arm 58 and is applied between ground and an inputterminal 60 of an electrical summing amplifier 62. The output signalvoltage Y of the integrating device 48 is applied between ground andanother input terminal 64 of the summing amplifier 62. The summingamplifier 62 is operative to electrically sum the output signal voltagesY. and (WY) and develop an output signal voltage W between ground and anoutput terminal 66. The output signal voltage W varies in accordancewith the extent of the surface undulations of the road 16 with respectto the plane 40.

Suitable recording means (not shown) may be connected with outputterminals 66 of the summing amplifier 62 for recording the output signalvoltage W on magnetic tape. Separate recording means (not shown) may beprovided for recording on magnetic tape the velocity of vehicle travelover the road 16 at the same time as the output signal voltage W isrecorded. The tape recording of velocity may then be compared with thatof the output signal voltage W in a manner to obtain a third magnetictape recording of output signal voltage W as a function of distancetravelled. Hence, constant vehicle velocity need not be maintainedduring recording.

The operation of the invention may be better understood from thefollowing description. Assume that the total frequency range of surfaceundulations of .the road 16 extends from F to F and that the breakfrequency of the spring 24 is F as indicated in the graphicalrepresentation shown in FIGURE 2. Then as the vehicle 18 is towed alongthe road 16 the wheel 12 will undergo displacements normally of theplane 40 due to the surface undulations of the road. Acceleration of thewheel 12 within the frequency range of F to F will be attenuated by thespring 24, and only acceleration of the wheel in the frequency range ofF to F will be transmitted by the spring to the mass 26. Theaccelerometer 28 will be responsive to the low frequency acceleration ofthe mass 26 and develop an output signal voltage Y which will be appliedacross the input of the integrator 48 to develop an output signalvoltage Y Hence, the output signal voltage Y will vary in accordancewith change of position of the wheel 12 with respect to the plane 40 dueonly to surface undulations of the road 16 within the frequency rangefrom F to F The displacements of the wheel 12 due to surface undulationsof the road 16 within the frequency range from F to F result in relativedisplacements between the platform 18 and the Wheel support 14 and whichare measured by the potentiometer 52. Hence the output signal voltage(WY) of the potentiometer will vary in accordance with the displacementsof the wheel 12 due only to surface undulations of the road 16 withinthe frequency range from F to F The output signal voltages Y and (W-Y)are applied between ground and the respective input terminals 64 and 60of the summing amplifier 62 for developing an output signal voltage Wwhich will vary in accordance with the extent of surface undulations ofthe road 16 with respect to the plane 40 over the entire frequency rangefrom F to F2.

Although the description of this invention has been given with respectto a particular embodiment, it is not to be construed in a limitingsense. Numerous variations and modifications within the spirit and scopeof the invention will now occur to those skilled in the. art. For adefinition of the invention, reference is made to the appended claims.We claim: 1. Means for measuring the extent of surface undulations of anobject throughout the frequency range of the undulations with respect toa reference direction and comprising:

surface contacting means adapted to traverse and maintain contact withthe surface of the object under ex- .amination,

acceleration responsive means adapted to be connected with a voltagesource for developing an output signal voltage variable in accordancewith acceleration of the contacting means normally of the referencedirection due to surface undulations below a predetermined frequency,frequency selective coupling means interposed between the accelerationresponsive means and the contacting means and adapted to transmitacceleration below the predetermined frequency and to attentuateacceleration above the predetermined frequency,

integrating means connected with the acceleration responsive meansresponsive to the output signal voltage developed thereby and operativeto perform a double integration thereof and develop an output signalvoltage variable in accordance with the extent of surface undulations ofthe object below the predetermined frequency,

displacement measuring means interposed between the contacting means andthe acceleration responsive means and adapted to be connected with avoltage 4. Apparatus for indicating the profile of a surface including:

i a body adapted to be displaced over the surface and including contactmeans for engaging the surface, support means, motion sensing meansmounted on the support means and responsive to displacement thereofnormal to the average plane of the surface to produce a first signalrelated to the displacement,

resilient means connecting the body and the motion sensing means fortransmitting relatively slowly occurring displacements of the body tothe support means and attenuating relatively rapidly occurringdisplacements of the body,

means operatively connected between the support means and the body forproducing a second signal related to relative displacement between thebody tions of a road throughout the frequency range of the undulationswith respect to a reference direction and comprising:

a vehicle including a rotatable member adapted to traverse the surfaceof the road under examination,

and the support means due to said relatively rapidly occurringdisplacements,

hold down means connected with the vehicle for prod Summing meansConnected t r iv t e first and viding a hold down force o th rot t blmember t second signals and responsive thereto to produce an maintainthe rotatable member in contact with the Output Signal representing bothrelatively slowly and surface of the road, rapidly occurringdisplacements of the body.

an accelerometer mounted on the vehicle adapted to be Appafatllsmeasuring reltltive displacements connected with a voltage o r fdeveloping an tween an inertial reference and a surface including:

output signal voltage variable in accordance with acceleration of therotatable member normally of the reference direction due to surfaceundulations below a predetermined frequency,

a vehicular mass,

motion sensing means mounted on the mass and responsive to accelerationthereof to produce a first signal related to the displacement of 'saidmotion a spring member connecting the accelerometer with the ensingmeans relative to the inertial reference,

rotatable member and adapted t t it d means for establishing a frequencyselective resilient tion below the predetermined frequency and to at-Support between the motlell sellslllg means and the tenuate accelerationabove the predetermined freh thereby to transmlt relatlvely Slowly Pquency, ring displacements of the surface to the motion integratingmeans connected with the accelerometer e and to attenuate relatwelyrapldly responsive to the output signal voltage developed occulgmgdlgpleicements d I d 1 thereby and operative to perform a doubleintegrameans or pro ucmga ff slgnal re ate to dlfsp tion thereof anddevelop an output signal voltage f i gggz zg fi gzi gg j zgg ig g gfzvariable in accordance with the extent of surface unzg g i 35 andresponsive thereto peroduce an dulations of the road below thepredetermined frequency,

a potentiometer connected between the rotatable member and theaccelerometer and connected with a voltmotion sensing means forproducing a first signal related to the displacement of the motionsensing means in the predetermined direction,

frequency selective coupling means mechanically connecting the body andthe motion sensing means and operative to transmit low frequencycomponents of displacement and to attenuate high frequency components ofdisplacement,

means for producing a second signal related to the output signalrepresenting the profile of said surface with respect to the inertialreference. 6. Apparatus for measuring relative displacements between aninertial reference and a surface including:

age source for developing an output signal voltage a hi lar ma Variab1in accordance the extent Of relative motion sensing means mounted on themass and redisplacements between the accelerometer and sponsive toacceleration thereof to produce a first tatable member due toacceleration of the rotatable i l l t d to th displacement f said motionmember above the predetermined frequency, sensing means relative to theinertial reference. and summing means connected with the integratingSurface Contact means,

means and the potentiometer for Summing the frequency selective couplingmeans mechanically con- P Signal Voltages developed thereby andOperative necting the motion sensing means and the surface to develop anp Signal Voltage Variable in contact means and operative to transmitrelatively cordance with the extent of surface undulations of l loccurring displacements of th Surface t the the road throughout thefrequency Tange of the 0 motion sensing means and to attenuaterelatively undulations. rapidly occurring displacements, Apparatus formeasuring displacements of a body means for producing a second signalrelated to displacein a predetermined direction Over a frequency rangements between the vehicular mass and the surface, eluding high and lowfrequency Components Comprising: 0 and summing means connected toreceive the first and second signals and responsive thereto to producean output signal representing the profile of said surface with respectto the inertial reference.

7. Apparatus for measuring the profile of a surface with respect to aninertial reference plane including:

a vehicular mass having a surface contacting wheel to be passed over thesurface,

motion sensing means disposed on the mass and responsive toaccelerations thereof to produce a first high frequency Components ofdisplaeement attemlsignal related to the displacement of said motionated by the coupling means, sensing means relative to the inertialreference,

and s mm g means connected to receive the first and frequency selectiveresilient coupling means connecting Second Signals and responsivethereto to Produce an the motion sensing means and the surface contactoutput signal corresponding to displacements of both wheel and operativeto transmit relatively slowly high and low frequency components.

occurring displacements of the surface contact means to the motionsensing means and to attenuate relatively rapidly occurringdisplacements, means disposed on said mass for producing a second signalrelated to displacements between the mass and the surface, and summingmeans connected to receive the first and second signals and responsivethereto to produce an output signal representing the profile of saidsurface with respect to the inertial reference.

Y No references cited.

DAVID SCHONBERG, Primary Examiner.

1. MEANS FOR MEASURING THE EXTENT OF SURFACE UNDULATIONS OF AN OBJECTTHROUGHOUT THE FREQUENCY RANGE OF THE UNDULATIONS WITH RESPECT TO AREFERENCE DIRECTION AND COMPRISING: SURFACE CONTACTING MEANS ADAPTED TOTRAVERSE AND MAINTAIN CONTACT WITH THE SURFACE OF THE OBJECT UNDEREXAMINATION, ACCELERATION RESPONSIVE MEANS ADAPTED TO BE CONNECTED WITHA VOLTAGE SOURCE FOR DEVELOPING AN OUTPUT SIGNAL VOLTAGE VARIABLE INACCORDANCE WITH ACCELERATION OF THE CONTACTING MEANS NORMALLY OF THEREFERENCE DIRECTION DUE TO SURFACE UNDULATIONS BELOW A PREDETERMINEDFREQUENCY, FREQUENCY SELECTIVE COUPLING MEANS INTERPOSED BETWEEN THEACCELERATION RESPONSIVE MEANS AND THE CONTACTING MEANS AND ADAPTED TOTRANSMIT ACCELERATION BELOW THE PREDETERMINED FREQUENCY AND TOATTENTUATE ACCELERATION ABOVE THE PREDETERMINED FREQUENCY, INTEGRATINGMEANS CONNECTED WITH THE ACCELERATION RESPONSIVE MENS RESPONSIVE TO THEOUTPUT SIGNAL VOLTAGE DEVELOPED THEREBY AND OPERATIVE TO PERFORM ADOUBLE INTEGRATION THEREOF AND DEVELOP AN OUTPUT SIGNAL VOLTAGE VARIABLEIN ACCORDANCE WITH THE EXTENT OF SURFACE UNDULATIONS OF THE OBJECT BELOWTHE PREDETERMINED FREQUENCY,